1. Field of the Invention
The present invention relates to a DC/DC converter configured to convert a DC voltage, and more particularly, to a DC/DC converter including a timer circuit.
2. Description of the Related Art
A related-art DC/DC converter is now described. FIG. 7 is a circuit diagram illustrating the related-art DC/DC converter.
The related-art DC/DC converter includes a comparator 504, an RS-FF circuit 113, a drive circuit 110, a reference voltage generation circuit 503, a timer circuit 501, NMOS transistors 108 and 109, a capacitor 107, a coil 106, resistors 103, 104, and 502, a ground terminal 100, an output terminal 102, and a power supply terminal 101.
The comparator 504 has an inverting input terminal for inputting a divided voltage obtained by dividing an output voltage Vout of the output terminal 102 and a non-inverting input terminal for inputting a reference voltage obtained by adding a ripple voltage, which depends on a power supply voltage and the output voltage Vout, and a slope voltage, which changes with a predetermined slope, to each other. The comparator 504 outputs a signal corresponding to the result of comparison. When the divided voltage is higher than the reference voltage, the comparator 504 outputs a signal of Low level to a set terminal of the RS-FF circuit 113. When the divided voltage is lower than the reference voltage, the comparator 504 outputs a signal of High level to the set terminal of the RS-FF circuit 113. A reset terminal of the RS-FF circuit 113 is supplied with a signal output from the timer circuit 501. An output signal is output from a Q terminal of the RS-FF circuit 113 in accordance with the output signal of the comparator 504 and the output signal of the timer circuit 501. The drive circuit 110 controls on and off of the NMOS transistors 108 and 109 in response to the signal from the RS-FF circuit 113, to thereby generate the output voltage Vout from the output terminal 102 (see, for example, Japanese Patent Application Laid-open No. 2011-182533).
In the related-art DC/DC converter, however, the reference voltage is generated based on the output voltage Vout, and hence there is a problem in that control is susceptible to noise from the output voltage Vout and is therefore liable to be unstable.